1. Field of the Invention
This invention relates generally to imaging systems, methods, and apparatus and more particularly relates to systems, methods, and apparatus for non-contact impedance scanning and imaging.
2. Description of the Related Art
Imaging provides valuable data on the properties and composition of materials and objects to a wide variety of individuals and enterprises including researchers, engineers, manufacturers, and medical professionals. Image quality is directly dependent on the resolution and contrast of the particular technology used to generate the image data.
Image resolution has been driven to the submicron-scale using small step scanning. Examples of this include atomic force microscopy (AFM), scanning electron microscopy (SEM), near field scanning optical microscopy (NSOM), etc. These methods are typically limited to providing surface profiles of the scanned matter. Similarly, image contrast has been improved through methods that penetrate an object such as fluorescence imaging, magnetic resonance imaging (MRI), and electrical impedance tomography.
For example, tomographic reconstruction has been used to create electrical impedance images of materials. These electrical impedance images can show useful information about human tissue composition enabling several medical applications including cancer diagnosis. However, the resolution of electrical impedance tomography is very low, limiting its usefulness.
The measurement of impedance differences in materials could potentially provide some of the largest measurable contrasts in the natural world. In particular, a high-resolution electrical impedance image of biological tissues could reveal a great deal of information due to the biologically significant behavior of electrically active ions (e.g., sodium, potassium, chlorine, and calcium), polar molecules (e.g., water), and inhomogeneous charge distributions (e.g., most proteins).
Measurements of electrical impedance of biological samples (including cells) can help illuminate both tissue structure and function, and can therefore play an important role in several medical applications such as cancer diagnosis and treatment. As early as 1923, Grant found that at 1 kHz cancer cells have a lower resistivity than normal cells. More recently, other applications have been suggested such as using impedance to classify breast lesions or to observe activity of white blood cells.
One prior art approach to collecting impedance data is direct contact measurement. Unfortunately, direct contact measurements may disturb or harm the material being tested. Furthermore, contact resistance can vary significantly with surface conditions of both the probe and the material resulting in inconsistent measurements. Consequently, direct contact impedance measurements on biological tissues have been crude and unable to provide data on a cellular size scale.
From the foregoing discussion, it should be apparent that a need exists for a system, method, and apparatus for high resolution measurement and scanning of the electrical impedance of biological and non-biological matter. Beneficially, such a system and method would provide valuable data for research, medical, and industrial purposes.